Corrosionpedia explains Billet

A billet is a section of metal used for rolling into bars, rods and sections. It can be produced with ingots or directly by continuous casting. Billets are used as raw materials or feedstock in extrusion, forging, rolling and other metal-processing operations.

Billets have limited use before they have been formed into more functional shapes and sizes. They must undergo a series of manufacturing processes before they can be used for various purposes. The unformed billets, however, can be used in striking currency such as coins and as reserves, similar to gold bars. Final products also include bar stock and wire. Centrifugal casting is also used to produce short circular tubes as billets, usually to achieve a precise metallurgical structure.

Billets have a specific grain structure, which enables the metal to be processed more intricately. Steel billets are also known for their malleability and ductility, especially when exposed to varying temperatures during shaping and molding.

Proper casting of billets is important because it determines the billet's strength and flexibility. Billets undergo a number of tests before they are sold. Billets that develop cracks and voids between heating and cooling processes are rejected, as such defects make the product useless.